1. Field of the Invention
The invention relates to a wire pressing method and apparatus for connecting a sheathed wire to a pressure terminal by press-fitting the sheathed wire into the pressing blades of the pressure terminal.
2. Related art
Conventionally, a wire is crimped to a pressure terminal using a wire pressing apparatus by press-fitting a sheathed wire into plate-like pressing blades of the pressure terminal using a pressing punch, each pressing blade having a slot into which the wire is press-fitted. This press-fitting force causes the edges of the pressing blades to cut the sheathed portion of the wire to expose the conductors and establish electrical connection.
A conventional example in which a wire is pressed onto a pressure terminal before attaching the pressure terminal to a connector housing wall be described.
FIG. 11 illustrates method for connecting a wire 40 to a pressure terminal 33 using a wire pressing apparatus 100. The method includes the following steps: setting the pressure terminal 33 on a pedestal 21 by forwarding catenated terminals 30; placing an end portion of the wire 40 on a wire connecting part 36 of the pressure terminal 33; and then lowering an applicator 10 by driving an air cylinder 12 to press and fix a barrel part 35 of the terminal with a terminal press 15 and simultaneously lowering a pressing punch 102 and an insulator crimper 17.
As a result of this operation, a wire pressing groove 104 of pressing section 103 at the front end of the pressing punch 102 abuts against the wire 40, and the conductors of the wire 40 are press-fitted into the slots of pressing blades 38. As a result, the sheathed portion of the wire 40 is cut by the respective pressing blades 38 to thereby establish electrical connection of the conductors with the connector. In addition, the upper ends of the pressing blades 38 are received in releasing grooves 105 arranged in the pressing section 103 so as to prevent displacement of the pressing blades in the longitudinal direction. Thereafter, the outer sheathed portion is fixed by crimping pieces 36a, so that the wire pressing operation is completed.
Next, a conventional example in which a wire is crimped to a pressure terminal after the pressure terminal has been received in a connector housing will be described. This wire pressing operation includes two stages: the first stage involves the step of attaching the pressure terminal to the connector housing; and the second stage involves the step of connecting the wire to the pressure terminal.
The first step of attaching the pressure terminal to the housing is such that longitudinally catenated pressure terminals wound in a reel are sequentially inserted into terminal accommodating chambers from the rear end of the housing continuously and then the catenated pieces are separated, as disclosed in, e.g., Unexamined Japanese Patent Publication Hei. No. 4-33285.
The second step of attaching the pressure terminal to the wire which is received in the terminal accommodating chamber is disclosed in, e.g., Unexamined Japanese Patent Publication No. Hei. 4-48568 and Unexamined Japanese Utility Model Sho. 61-136484.
In more detail, as shown in FIG. 12, a pressure terminal 108 is inserted from the rear into the forward portion of housing 106. At this instance, since a downwardly projecting retaining lance (not shown) is provided at the front end portion of the pressure terminal 108, an appropriate clearance is provided in the upper part of the terminal accommodating chamber between adjacent cavity walls 122.
The pressure terminal 108 is fixed at a correct position by a positioning jig, and then the wire 40 is press-fitted into pressing blades 107 by the wire pressing apparatus 110 having the pressing punch 102 that is fixed on a vertically movable applicator main body 113 from above. At this instance, the sheathed portion of the wire 40 is cut by the edges of the pressing blades 107, so that electrical connection is established. It may be noted that the wire pressing groove 103 in which the sheathed portion of the wire is received and the releasing grooves 105 for avoiding interference with the pressing blades 107 are formed in the front end of the pressing punch 102.
However, with reference to FIG. 13, the following problems are encountered when a wire is crimped onto a pressure terminal before attaching the pressure terminal to the housing. If the sheathed portion of the wire 40 is thick or the sheathing material rigid, or if the pressing blades 38 do not perform the cutting function satisfactorily, then the wire pressing groove 104 is abutted against the wire 40 by the lowering of the pressing section 103 of the pressing punch 102, thereby press-fitting the wire 40 into the slots 39, and as a result of the press-fitting operation, expanding force P is applied to the pressing blades 38, thereby causing a pair of confronting pieces 38a constituting the slot 39 of each pressing blade 38 to be expanded outwardly.
As the confronting pieces 38a are further expanded, the pressing blades 38 are plastically deformed, which in turn reduces or eliminates the pressing force applied to the wire 40 by the pressing blades 38. That is, once the pressure terminal 33 has been plastically deformed beyond the limit of elastic deformation, it is likely that electrical conduction between the wire 40 and the pressing blades 38 will not be established. Further, even within the limit of elastic deformation, it becomes difficult to attach the pressure terminal 33 to the housing if a width W between the pressing blades 38 in the expanded condition is larger than the width between cavity walls (not shown) of the housing.
As described above, the pressing blades 38 are likely to be expanded in the conventional wire pressing apparatus, and this may lead to inconvenience in that the expanded pressing blades 38 cause side walls 37 to incline outward or that, in some cases, it becomes difficult to insert the pressure terminal 33 into the housing.
With reference to FIG. 14, the problems encountered when the wire is pressure crimped to a pressure terminal after having attached the pressure terminal to the housing are as follows. By way of example, if the sheath of the wire 40 is thick or the sheathing material is rigid, or if the pressing blades 107 do not perform the cutting function satisfactorily, then the side portions of the pressing blades 107 are expanded toward the cavity walls 122 of the housing 106 as the wire 40 is press-fitted by the lowering of the pressing punch 102. In addition, once the pressing blades 107 have been plastically deformed and have therefore lost restitutive force by going beyond the limit of elastic deformation, necessary contact cannot be provided, which in turn makes it unlikely that a connection providing electrical conduction between the conductors of the wire 40 and the pressing blades 107 will be implemented.
Still further, since the expanded pressing blades 107 cause the cavity walls 122 of the housing to incline, cavities adjacent thereto are affected, or, in some cases, it is likely that the pressure terminal cannot be connected to the wire by pressure.
Therefore, for the aforementioned reasons, problems such as a reduction in the yield of a mass production process, a curtailed designing freedom due to a restricted use of materials, and an increase in the cost of manufacture are encountered.
The invention has been made to overcome the aforementioned problems. Accordingly, the object of the invention is to provide a wire pressing method and apparatus for a pressure terminal which is capable of connection of a wire by not only allowing electrical conduction to be established between pressure terminals and wires of differing standards, but also preventing pressing blades from being expanded at the time of a pressing operation.